<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      let p = new Promise((res, rej) => {
        setTimeout(() => {
          res('66');
        }, 100);
      });

      p.then((value) => {
        return new Promise((res, rej) => {
          res('666');
        });
      })
        .then((value) => {
          console.log(value);
        })
        .then((value) => {
          // undefined
          console.log(value);
        });
    </script>
  </body>
</html>
